It is common practice in fields and industries that require pulling metal cable or metal rope through space to use a cable gripping mechanism that includes the ability to grip and release the cable on demand, so the cable can be pulled through space. Oftentimes, the pulling apparatuses utilize a pair of gripping mechanisms, one gripping while the other is released so the cable can effectively be pulled “hand over hand.” In these circumstances the gripping mechanisms work in tandem to create a winching mechanism or system for intermittent and continuous heavy pulling, lifting and lowering.
Ideally, the grip and release mechanism is designed to prevent the cable slipping backwards, particularly during a cable pulling recovery stroke. This is also known as a “non-slip” system. The mechanisms typically include a gripper having an inner surface that defines an aperture or axial channel or bore dimensioned to receive the cable or wire rope, and lined with “teeth” that bite the cable and hold it in position as the gripper is forced down on to the cable surface. These “teeth” typically are created by means of serrations or threaded ridges on the cable engaging surfaces of the axial channel.
Many gripper mechanisms typically in use in the art work on a nested wedge principle that provides a structural means for translating the force applied in cable pulling to the cable grippers themselves. Here the cable or wire rope is sandwiched between member segments that together define a wedge set. Generally, the wedge set has an overall triangular shape, typically defined by two gripper members, or it can have an overall frusto-conical shape defined by a plurality of gripper members, typically two-four members. The wedge set is nested in, or fits within, a cavity or recess that comprises part of the cable pulling apparatus and is dimensioned to receive the wedge gripper set. As the wire rope is pulled, the wedge set is forced into the cavity or recess, the wedge set outer edges sliding along the tapered inner surface of the cavity or recess such that the wedge pieces are forced down onto the cable or wire rope surface, squeezing the cable or wire rope, and biting the rope with gripper “teeth”.
Cable pulling force typically is provided hydraulically, moving the cable pulling apparatus component that houses the gripper wedge recess during the pulling stroke. As the recess housing is pulled forward, the gripper wedge set is forced into the recess and onto the cable surface, gripping the cable and pulling it forward with the housing. Thus the nested wedge system provides a structural means for translating the cable pulling force provided by the hydraulics to the cable grippers themselves for gripping the cable.
To be functional, a cable gripping mechanism also preferably includes some means for supporting the gripper members in moving in unison on and off a cable surface so as to provide substantially even pressure on the cable, as well as some means for limiting the distance the gripper members can move off the cable. Gripper member linking means in use in the art can include a mechanical link such as a yoke that connects the members together. Other linking means can include magnetic means positioned between the cable gripping members. Still other means used in the art can include a direct, timed connection between the individual cable grippers and the cable pulling apparatus itself. Such connections can include mechanical or hydraulic connections.
Gripper member limiting means in use in the art typically include mechanical range-able or extensible limiters. Examples include elastomers linking gripper members or a gripper yoke to the pulling apparatus; compression springs; telescoping means, including pistons, and the like. U.S. Pat. Nos. 5,015,023; 6,305,880; and 2016-0348807; Chant Engineering's “Wire Rope Grips”, https://chantengineering.com/products/wire-rope-grips/; and Pow-r Mole Sales LLC cylinder-activated jaws, http://www.powrmole.com/bursting-and-boring, are representative of the art.
In part because of the great force placed on the cable as it is being pulled (typically, cable pulling machines can have a pulling force of anywhere from about 6 tons to 100+ tons) the cable can have a tendency to twist as it is pulled, making it difficult for cable gripping mechanisms in the art to maintain an even grip or even pressure on the cable. Thus cable gripping mechanisms or systems in the art, including nested wedge gripper systems that rely on a structural force translation means to move the grippers into position on a cable, can be subject to great wear and tear, and can have a tendency to seize, and/or require the need for anti-seize lubricants to allow them to function properly in the field. Another impact of the great force nested wedge gripper systems in the art can apply to cable or wire rope surfaces is that they can “bite” the cable so strongly they can cut the individual wire strands, fraying the rope or cable on its lateral surface, and thereby weakening the cable.
Existing gripper systems often are multi-piece systems that can be complicated or cumbersome to install, especially in a vertical pulling system. One drawback of existing gripper mechanisms is the number and complexity of components to the mechanism that can break in the field, in part due to the high pressure exerted on them, and the difficulty in keeping tension even on the cable from multiple gripper members. The multiplicity of independent components also can make the gripper mechanisms difficult or cumbersome to install, remove or repair, especially in the field. Sliding wedge components can have a tendency to seize and so can require use of anti-seizing compounds applied to them and/or the cable surface, making the grippers difficult to clean. In addition, these systems typically are open systems, and debris can get caught between the gripper members and the tapered or sliding surface, making seizing more likely and/or otherwise impeding proper movement of the members and even pressure on the wire surface. Cleaning the debris out in the field can be cumbersome at best, and often difficult. Keeping the system in good working condition in open systems typically requires taking the components apart and carefully cleaning out debris and excess grease or lubricant, also a tedious and cumbersome activity.
In large wire rope nested wedge gripping systems, proper cleaning can be especially difficult. Moreover, where the timing and/or gripper limiting means is provided by a separate hydraulic system, this additional system with its own maintenance and power needs, also needs to be maintained and managed in the field.
In addition, some gripping mechanisms work only in a vertical or horizontal system, but not both. This can be a drawback in designing pulling or winching systems for multiple applications where it can be advantageous to utilize a range of pulling positions for different operations. It would be advantageous to have a “universal” gripper system that can work in either a vertical or horizontal position without modification. It also would be advantageous for the gripper system to be able to occupy both the “front” holding position and “rear” pulling position without modification, for use in tandem cable gripper systems where the grippers form part of a “hand over hand” cable winching system with front and back cable grippers that alternately grip the cable to pull the cable during the pulling stroke and hold the cable from slipping backward during the recovery stroke.
There remains a need for a grip and release wire rope or cable gripper system that provides substantially even pressure along a cable gripping surface during operation, that is not subject to seizing, and that minimizes cable fraying. There also remains a need for a gripper system that does not rely on a nested wedge system or other structural means for translating force to the cable grippers; that can be applied in both horizontal and vertical systems, and that can be used in both a cable pulling and cable holding position without modification. There also remains a need for a gripper system that does not require a tapered sliding surface to support engaging and gripping a wire rope surface, that does not “bite” a cable side surface excessively, and that is not subject to seizing, even under high pulling forces. Finally, there remains a need for a gripper system that can be installed as a unit; that is easy to use and maintain; that has few moving parts; that is less subject to wear and tear; that is small and compact; that can be fabricated as a “closed system” such that the force translation means is not impacted by debris in the field; and that does not require application of anti-seizing lubricant to the gripper or cable surfaces.
The present disclosure describes improvements in metal cable or rope gripping mechanisms and methods of use thereof that overcome deficiencies in the mechanisms and devices of the prior art.